Search Documents

This paper reviews the current techniques employed in the prediction of subsidence and how they have been applied to partial extraction systems. The method using influence functions to describe the shape of the profile is investigated in detail and has been adopted to model the subsidence over workings in Huntly. It is compared with the profile methods developed in the United Kingdom and found to predict the subsidence profile more accurately than these methods.

Jan 1, 1991

By Malcolm Powell

"The argument has long raged across the oceans as to what the best AG/SAG mill aspect ratio is. The North American practice of a high aspect ratio of two, diameter twice length, through to the South African and Scandinavian practice of an aspect ratio of as low as a 0.5. Within the collaborative P9 AMIRA project the MPRU of the University of Cape Town and the JKMRC of the University of Queensland have been collecting plant data pertinent to this issue over the past four years.The JK SAG mill model developed by the JKMRC is based upon data collected from mills having a range of aspect ratios from 1 up to 2. The maximum mill speed, mill load, and ball filling in the fitted data base were all below the operating range common in South Afr-ica. The extension of the P9 project into South Africa therefore lent an ideal opportunity to collect data in a whole new window of operation that would allow the range of applicability of the semi-empirical SAG model to be greatly extended.At the heart of the differences in aspect ratio is the completely different operating practice for high- and low- aspect mills. The mill filling, mill speed, and recirculating loads of closed-circuit single-stage operation have more influence on the differences in operation than the pure aspect ratio relationship. Relationships for load have been extended to 45% filling, with the modified model showing the measured peak in throughput as the mill filling increases. The ball load relationship now covers fillings of over 30% balls (of total mill volume), thus including so-called SAG-ball mills. The influence of closed circuit operation has been measured. It has been found that a key issue of the high slurry flows associated with closed circuit operation, especially when closed with a cyclone, is the pulp discharge limitation of the traditional grate and radial lifter configuration. It has also been observed that absolute mill length is more of an issue than aspect ratio. Slurry flow along the mill and charge segregation within the load are being investigated on pilot and full-scale mills to provide data for potentially modifylng the perfect mixing model that is used for the SAG mill.Improved understanding of these aspects of SAG mill operation and extension of the JK SAG model to better cover the entire range is allowing serious direct comparison of high- and low aspect mills for the first time. It is the conclusion of the researchers working in this area that there is no one best practice, that in fact mills across the range have their application based on ore type, desired product, available capital and on operating costs. Developing robust designs allows direct comparison of two-stage circuits using high-aspect primary SAG mills, with single-stage closed circuit low-aspect SAG mills. The new operations within South Africa are now considering both circuit types, and data is presented on selections that cover the full range of aspect ratio and operating practice."

Jan 1, 2002

By KEITH BARRONI

In the proposed criterion for coal a distinction is made between brittle and "psuedo-ductile" failure. This criterion is the basis for the development of new equations for coal pillar strength, including a transition from brittle fracture to pseudo-ductile yielding. In addition the equations obtained allow the critical minimum pillar dimensions to be calculated to avoid "catastrophic" and "ultimate failure".The validity of these formulae can be tested by comparing their results with pillar case histories derived from the literature.

Jan 1, 1988

The work described herein is the opening phase of an extensive system of underground excavation undertaken under contract with a Malayan authority.The specifications called for the lining of all tunnels in earth or broken rock with circular segmented cast iron lining, similar to that of the London tubes, and it is the installation of these linings which it is proposed to discuss.Owing to the long deferred delivery quoted and the obvious need for speed of access to the internal installation, it was decided to defer driving the completed circular section and substitute two small timbered headings.These could later be opened out in turn to full section and lined without prejudice to traffic, since both of them had access to the internal workings.NATURE OF ROCKThe rock series through which the circular sections were driven consisted of:(a) A wide zone of intrusive porphyritic granite, consisting generally of orthoclase phenocrysts in a ground mass of micro pegmatite. This area showed advanced weathering, varying from a stage showing slightly tinted kaolin containing approximately 20% of small boulders to one of ultimate decomposition to pure kaolin;(b) A narrow zone of weathered augite diorite, consisting of rock masses of a maximum weight of some 100-150 tons, isolated by clay seams up to 1 ft. 6 in. in width.The whole area was in a state of quasi-hydrostatic equilibrium, which resulted in heavy pressure immediately after excavation. Freshly broken faces would appear to be quite solid but, within a few minutes, would commence to sweat and "slab off" under pressure and, unless support was placed promptly, the whole face would burst out and run from above. Mucking was slow, owing to the plastic nature of the clay and the ease with which it puddled into slurry.In zone (b) a good deal of trouble was experienced because of the fact that the somewhat heavy blasting necessary tended to cause movement of the large rock masses. Subsequent scouring out of the supporting clay bands by the waterflow permitted settlement of the ground on to the timbers and many reinforcing sets were therefore required.The timbering of the pilot headings and its relation to the cross-section of the circular tunnels is shown in Fig. 1. Top and side spiling was driven in the ordinary way, but in bad ground intermediate sets and breast boards had to be placed. These sets were usually withdrawn after the...

Jan 1, 1941

By B. P. Faulkner, M. Weinecke

Svedala started a development program in 1997 to develop a process to convert waste tires into valuable commodities. A review of numerous approaches revealed short-comings in the various approaches either process, mechanical, combination of factors, or trying to emphasis the production of low value products. A market study revealed that a process that could produce a good grade of carbon black would be economically feasible. This paper discusses the laboratory and pilot plant development and commercial plant design.

Jan 1, 2001

By Albert Ruiz

South Coast Water District (District) operates the Beach Interceptor Sewer Tunnel (BIST) in South Laguna, Orange County, California between Mon-arch Beach and Aliso Beach (Figure 1). The 10,424-foot long BIST houses a 24-inch Techite gravity sewer pipeline critical to the District Sanitary Sewer Collection System that conveys 1 MGD of raw sewage to a wastewater treatment plant. The original tunnel was constructed in 1954 and the sewer line replaced in 1974. Periodic inspections by sewer pipeline maintenance crews have documented deterioration of specific intervals of the tunnel within the past few years (Sancon 2003). Rotting timber supports and rock falls in the tunnel as a result of the deterioration were endangering the sewer pipeline. A 50-foot section of the tunnel was determined to be in need of immediate repairs, which were carried out from January to August in 2007. This section was enlarged to a horseshoe shape and lined with shotcrete. The pipe was encased in concrete in the invert of the new enlarged cross section. Hatch Mott Mac-Donald (HMM) designed the emergency repairs, carried out an assessment of the rest of the tunnel alignment, and is currently developing a work plan for rehabilitating the entire tunnel.

Jan 1, 2008

By M. Prats

Most of the information available on the heat efficiency of hot fluid injection processes, both water and steam, has been obtained from calculated temperature distributions in the pay zone and adjacent formations. The usual approach has been to write the heat balance equations in terms of the temperatures, and then to introduce whatever simplifications are necessary to help obtain an analytical or a numerical solution. In either case, the assumption has often been made that the vertical thermal conductivity in the flooded interval is infinite, so that the temperatures within the flooded interval are then independent of vertical position. Because it was first made by Lauwerier,l and has been used extensively since, this assumption will be referred to as the Lauwerier assumption. Excellent reviews of the literature on the heat efficiency of hot fluid injection processes have been given by Spillette,2 Flock et al.,3 and Ramney.4 Of course, the most significant contributions take into account the effect of a finite vertical thermal conductivity on the vertical temperature profile. The most general analytic expression for the heat efficiency of a hot fluid injection process is that of Antimirov5 who considers injection of a heated incompressible fluid into a reservoir through an arbitrary number of wells. The rate of heat injection into the reservoir, as well as the injection temperature, is an arbitrary function of time. The geometry of the horizontal flow is arbitrary, although the reservoir is considered to be of uniform thickness and properties and to be of infinite areal extent. Heat transfer within the reservoir is by horizontal convection and conduc- tion, and by vertical conduction. In the formations adjacent to the flooded interval, heat transfer is by conduction in any direction. Thus, the available expression for the heat efficiency due to hot water injection has been developed for rather general conditions. This degree of applicability has not been obtained for other thermal recovery processes. By making the Lauwerier assumption we have been able to obtain expressions for the heat efficiency that are essentially independent of the thermal recovery process, be it steam, hot-water, or underground combustion. Clearly, then, the approach followed here is more restrictive than that of Antimirov5 in that it uses the Lauwerier assumption. At the same time less restrictive assumptions are made about the horizontal heat transfer mechanisms, either in the flooded interval or in the formations adjacent to it. The main difference between our approach and that of other investigators is that the heat balance in the pay zone is expressed for the pay zone as a whole rather than for a volume element within it. The Lauwerier assumption is introduced after the problem is developed along these lines as far as possible. The details of the development of the heat efficiency are given in the Appendix, while the main features of the model are discussed in the next section. Results and their implications are discussed later in a separate section. The Model Certain assumptions have been made to determine

Jan 1, 1970

The Geological Resource Map of New Zealand (GERM) is a computerised inventory of aggregate, mineral, coal, petroleum and thermal water occurrences, containing summary information on location, production, geology, and geochemistry. The types of occurrences include quarries, mines, gold dredges, wells, outcrops, seeps, springs, and fields. The file contains entries for about 10,300 sites and is used to produce tables of data and maps at any scale, for single or multiple commodities. The published format is the New Zealand 'Geological Survey map series Geological Resource Map of New Zealand 1:250 000'. Seventeen of the 27 map sheets covering New Zealand were published by August 1991, with three more close to publication.

Jan 1, 1991

By D. S. Pye, J. P. Gallus

Successful hydraulic pressure treatment of oil and gas wells that have long producing intervals, multiple pay zones, fluid thief zones, or natural or induced fractures has long been a serious problem plaguing the petroleum industry. High fluid-injection rates, straddle packers, ball sealers, and either liquid or solid additives to the treating fluids are being used to cope with this difficult and costly problem.l-6 The use of ball sealers and straddle packers is limited, in practice, to wells that have been completed with perforated cemented casings or liners. Well stimulation with ball sealers and straddle packers is usually successful as long as the cement remains competent. The other techniques of diverting are used with all types of completions. However, there are two significant disadvantages of the high rate method: excessive horsepower requirements, and the need of large treating-fluid volume. Consequently, most well stimulation techniques that involve diverting depend upon ball sealers or granular materials. Liquid diverting agents, and some of the solid ones in use today, frequently will cause formation damage. On the other hand, the most popular particulate diverting agents often are so soluble in the treating fluid that they become largely ineffective; their particle size is severely reduced as they dissolve while being transported through thousands of feet of pipe to the formation face down hole. In our attempts to deal with the shortcomings of these diverting agents, we experimented with a large variety of potentially suitable deformable materials the solubility of which could be controlled. Following are the criteria for the diverting agent sought: 1. The material must be effective in reducing fluid loss to thief zones, including existing fractures and very high permeability layers in the formation to be pressure treated. 2. The material must have enough strength to bridge under the treating pressure. 3. The material must be insoluble or slowly soluble in the treating fluids so that the particles retain sufficient size to be effective after they reach the formation face. 4. The material must be completely soluble in the produced oil or condensate liquid so that it can be removed readily; it must not cause formation damage. A number of products consisting of various polymers blended with waxes and other solid hydrocarbons were examined. All these materials satisfied the criteria for a diverting agent and also exhibited some degree of plastic deformability. On the basis of initial tests of strength and hardness, several blends of wax and polymer were selected for extensive testing in the laboratory and the field. These compounds have congealing temperatures ranging from 140 to 190F; they are insoluble in water and soluble in oil. They conformed, therefore, to the criteria specified for a theoretically superior diverting agent. Laboratory and field tests were conducted using these wax-polymer materials to demonstrate that the use of a deformable diverting agent can significantly improve fluid diverting performance. Data in this

Jan 1, 1970

SOME notes on the works of the Electrolytic Refining and Smelting Company of Australia will no doubt be of interest to members of the Institute, more especially as much of the work is new to Australasia. As many of the members who may read this paper have not been in a position to visit works of this kind, and are consequently not thoroughly acquainted with all the operations carried on, the author has taken the liberty, in some cases, to enter into explanation which would otherwise be unnecessary. The works are situated at Port Kembla (New South Wales), about fifty miles south of Sydney, and are approachable both by rail and water. The Government has recently built a low-level jetty upwards of five hundred feet long, and intends installing at an early date an electrically operated portable crane to facilitate the handling of material to and from the boats. This will mean: a considerable reduction in the length of time that boats are laid up at the jetty. There are also under construction two breakwaters, which, when complete, will materially assist shipping operation...

Jan 1, 1910

By Dae S. Young

The paper point out a new procedure to calculate the volumetric distribution of rock fragments. The method combines the practicality of digital image processing of the rock surface with the theoretical volume calculations based on principles and laws of fractal geometry. The final volumetric distribution curve is compared with the results from traditional sieving indicating close agreement.

Jul 17, 2000

The case study has identified and characterised additional subsidence arising from longwall mining above or under existing longwall goaf. It suggests that the magnitude, mechanisms and prediction methods for such additional subsidence are different between the two mining configurations. This paper presents a proposed method to predict maximum vertical subsidence due to longwall mining under existing longwall goaf. It suggests that, unless different results from further new cases become available, the findings presented in this article, including the aforementioned prediction method, be applicable to the majority of sites in New South Wales, where multi-seam longwall mining is to take place. This article also presents an important concept of 'overburden modification' due to multi-seam mining. A causal relationship between the above-mentioned additional subsidence and 'overburden modification' has been identified as a result of the case studies. Further investigations into the physical processes that cause such overburden modification will be fundamental to the understanding and management of multi-seam subsidence.

Nov 25, 2010

The Rosebery and Hercules mines, situated in the Rosebery-Williamsford district in western Tasmania, have a history of production dating back to 1896-7, although full scale production did not commence until 1936, following the development of a satisfactory process of selective flotation (Hall, Cottle, Rosenhain and McGhie, 1953). The mineral composition of the Rosebery zinc-lead ores was first described in detail by Stillwell (1934). The Hercules ore is generally similar, but as yet no descriptions of it have beenpublished.Since Dr. Stillwell's paper appeared, the management of the Rosebery and Hercules mines has from time to time submitted a number of interesting mineral specimens to C.S.I.R.O. Mineragraphie Investigations. Examination of these specimens brought to light eight minerals, some relatively uncommon, not previously recognized in these ores.They are cassiterite, molybdenite, stannite, electrum, meneghinite, boulangerite, pyrargyrite and pyrrhotite. Some of the specimens are also rich in tetrahedrite and gold. In addition each of the other ore minerals described by Stillwell, viz. pyrite, sphalerite, galena, bournonite, chaleopyrite and arsenopyrite, was detected in one or more of the specimens examined during the present study. The principal gangue minerals were found to be quartz, manganiferous carbonate, sericite and barite, agreeing closely with the observations of Stillwell.The present study was based on the examination of the following eight specimens.

Jan 1, 1960

By J. H. Kim

Since the Hardy Cross numerical algorithm was applied to the solution of mine ventilation networks, there have been numerous developments in ventilation network analysis procedures. The Newton-Raphson method, the linear theory method, and the second-order approximation method are three of the additional approaches that have been applied. The efficiency of a ventilation network analysis procedure depends not only on the method of solving the system of equations derived from ventilation networks, but also on the method of deriving the equations through selection of the meshes. This paper investigates the impacts of three mesh selection methods on the efficiencies of four ventilation network procedures. The minimum-resistance spanning tree method is the most popular procedure for selecting meshes. The shortest-path method was suggested by Epp and Fowler (1970) for improvement of the Newton-Raphson method. The minimum-resistance-path method is suggested here as the third method of selecting meshes. The effects of these three methods on the Hardy Cross method, the Newton-Raphson method, the linear theory method, and the second-order approximation method are analyzed in this paper. These network analysis methods have been summarized in the paper by Kim and Mutmansky (1991).

Jan 1, 1992

By A. M. Hearn, J. G. Roos

Energy consumption, being a large proportion of the input of the ferroalloy production process, can be measured in terms of the efficiency with which the energy is utilized and the effectiveness with which it is used. The efficiency of the usage of energy revolves around the specific consumption of the energy for the production of the alloy, which encompasses the thermodynamic aspects of the process and is more of a metallurgical function that will not be addressed further in this paper. The effectiveness with which the energy is utilized is determined by the optimisation of the electricity supply from the utility (in this case Eskom). The South African electricity supply industry is on the brink of considerable restructuring, implying changes in ownership, structure and regulation. In other countries, however, restructuring has often seen higher prices. Owing to the diversity of growth prospects in South African markets, Eskom is turning to new market management and generation strategies. In future, Eskom will develop pricing strategies to increase demand from attractive customer segments such as paper & pulp, iron & steel, aluminium, and other metallurgical industries. There will be a broader spectrum of product offerings, including dynamic pricing options and demand-side management incentives. In a future electricity market that will become more dynamic and demanding, it will become increasingly important for electricity consumers to optimise their electricity supply. There are many facets in optimising the electricity supply, which include optimal utilisation of the tariff, integrating energy cost management into the production planning process, implementation of demand-side management actions, modelling, scenario planning (.what-ifs?.), optimisation, maintenance scheduling coordinated with the tariff periods, etc. This paper gives consideration to the status of the development of technology at the manganese alloy works of Samancor at Meyerton, South Africa in order to increase the effectiveness with which energy is utilized.

Jan 1, 2004

By A. W. Ruff

The seismic wave produced by an explosive is very important in blasting. A true understanding of the wave is only important when considering possible structural damage to buildings located near the blast, but it is also of primary importance when considering rock fragmentation. Because of the importance of the seismic wave to fragmentation, a finda-mental study of the seismic wave and its effect was made at the Cananea Consolidated Copper Co.'s mine at Cananea, Sonora, Mexico. Strain gages were used to measure the strain in the rock when nearby explosive charges were detonated. The variance in the circuit voltage caused by changes in the resistance of the strain gage was measured with an oscilloscope and recorded with a Polaroid camera. CONFINED DRILLHOLE CHARGES To record the seismic wave from a confined drillhole explosive charge, a gage was cemented to the bottom of a 4-in diam drillhole. The horizontal gage hole and nine horizontal charge holes were drilled perpendicular to the center line of the 2-39 drift and 4 ft above the floor. The gage hole was 29 in. deep, and the charge holes were drilled so that each bottomed 1 in. deeper than the gage hole. The gage was installed with its axis horizontal and parallel to the 2-39 drift. The charge holes had the following horizontal distances from the gage: hole 3, 3 ft; hole 4, 4 ft; hole 5, 5 ft; hole 9, 9 ft; hole 10, 10 ft; hole 14, 14 ft; and hole 15, 15 ft. Figs. 1 and 2 show the relationships of the gage and the charge holes. Charges of 80 pct special gelatin, which weighed 50, 100, and 150 g were exploded in the charge holes and the seismic waves were recorded. All charges were stemmed with 200 g of mud and detonated with an electric blasting cap. Fig. 3 shows the recorded seismic waves. The reflected components of the waves were too weak to be objectional on these records. Table I shows the data taken from the wave forms. The approximate average velocity of a wave with a 9-ft travel distance was 12,900 fps. Since different charge weights were used, it was necessary to scale the data. The scaled maximum compress ion-strain data and the scaled maximum tens ion-strain data are shown in Figs. 4 and 5, respectively. Figs. 6 and 7 show the strain-distance data from Figs. 4 and 5 converted to a 1-lb charge. The results showed that the wave consisted of an initial compression pulse followed by a tension pulse. The amplitude of the tension pulse approached the amplitude of the compression pulse as the distance between the gage and the shot increased. The decay rate of the seismic wave is very important in the evaluation of the blasting characteristics of a rock. When high-amplitude stresses are produced, as in rock fragmentation, the rate of decay is much more rapid than when small amplitude stresses are produced. In underground mine blasting, the burdens are usually not greater than 6 ft and the decay is very rapid. The rapid seismic-wave decay rate in the fragmentation range means that in practice, if the minimum weight of powder is used to break a specified burden, only a very

Jan 1, 1961

By Alain Blouin, Mohamad Sabsabi, Aissa Harhira, Paul Bouchard, Greg Lithgow

"The objective of this study was to demonstrate the application of Laser-Induced Breakdown Spectroscopy (LIBS) to the continuous analysis of online monitoring of Al, Mg, Ni, Mn, Si and Fe in nickel ore limonite and saprolite slurry samples. Analysis was performed on slurry samples in air at atmospheric pressure. Two pure samples of limonite and saprolite were used. Mixtures of the two samples in varying proportions were used to build calibration curves, study the influence of solid/liquid ratio, and evaluate short and long term reproducibility. The LIBS measurement of these elements is independent of the water content (from 70-85%, the range allowed by our setup). Repeatability of the measurement and long term reproducibility (from day-to-day) were below 1.2 % and 2% respectively for all the elements studied in our conditions. The results obtained showed that an industrial LIBS analyzer could provide the chemical composition of the six elements Al, Mg, Ni, Mn, Si and Fe within 1-2 minutes.IntroductionThe metal-producing industry faces the major challenge of increasing productivity, reducing costs, and maximizing benefits from existing equipment. By pyrometallurgy, metal making involves the basic steps of charging the furnace, melting the charge and refining. By hydrometallurgy, the metal refining is carried out through the dissolution of the metal by chemical reaction and electrolysis. During refining either by pyrometallurgy or hydrometallurgy, it is critical that operating parameters be adjusted and controlled so that the chemistry of the melt or the solution is within predetermined limits. Presently, the complete turnaround time for sampling, sample transfer, analysis and communication of the results to the operators is often 30 minutes or more."

Jan 1, 2016

By A. W. Asman

The problem of balanced design in a belt conveyor has been under constant study. Increased use of this method of transport in recent years has stimulated investigations. Conveyor belt, power transmission and other machinery should be adequate to perform the required service. All components of the belt conveyor should work as an efficient unit moving its load continuously between terminals. As part of a long term research project on belt conveyors, Hewitt-Robins established in 1954 a 2-year grant at Pennsylvania State University. Under terms of the grant, certain fundamental phenomena were to be studied. This work evolved a new concept in belt conveyor power determination based on the principle of belt tension. The Penn State contract furnished the foundation for later more detailed studies. From these most recent investigations, more specific factors were defined. In the final analysis, all of the data collected has been worthwhile in belt conveyor design. Units now operate over long distances at speeds of over 800 fpm. Long high lifts are commonplace. Where vertical or inclined shafts were the rule, belt conveyors receive first consideration. Although belt conveyors have moved forward rapidly, the future will see a tremendous gain in their use. The ideal test belt conveyor would be several thousand feet in length and have a maximum tension of at least 70,000 lb., Also, this conveyor should be horizontai and have a variable feed rate of more than one material. Data from such a field belt conveyor combined with laboratory information would permit accurate analysis. Since this type of conveyor was not available, many field locations were visited: An alternate would have been to erect a closed circuit system in the laboratory. Either method had limitations and the first was selected as having the best possibilities. Manufacturers of conveyor belting and machinery basically have been using the same horsepower formula. As more information became available from field installations, factors in the basic formula were modified. Practically all conveyors are designed today by adding together the horsepowers required to move the empty belt, move the load horizontally, and elevate the load. In selecting size of drive motor, the first two elements are relatively unimportant if the last is large. However, it is the combination of

Jan 1, 1961

By W Dodson, S Dogramaci

Isotopes and hydrochemistry were used to define groundwater flow systems and better understand the hydrogeological setting of the Karijini National Park, which is in the Central Pilbara region adjacent to the Marandoo iron ore mine. Based on the stable isotope composition of the water samples, the data can be divided into two main groups. Groundwater is characterised by depleted dD and d18O, suggesting no significant evaporation effect. Surface water on the other hand is more enriched in dD and d18O due to evaporation. The relatively high concentration of Cl- compared to rainfall and depleted dD and d18O values of groundwater indicate that recharge of the aquifers is occurring during intense rainfall events when rapid infiltration occurs. Evapotranspiration then acts to concentrate ionic species prior to recharge. Relationships between the major ion concentration and catchment area, surficial Tertiary cover and distance between recharge and discharge were identified. The results show that these catchment variables combine to determine unique water chemistry for each sub catchment in Karijini National Park. The TDS concentration of the groundwater in the Marra Mamba Iron Formation that hosts the Marandoo ore body is higher than most of the water bodies surrounding the mining area suggesting significant modification or different recharge mechanisms to that of the Karijini groundwater.

Jan 1, 2009

North American Coal is a subsidiary of NACCO Industries. Originally founded as Cleveland and Western Coal in 1913, North American Coal took its present name in1925. Today, North American Coal is one of the 10largest coal producers in America, mining about 32Mt/a (35 million stpy). The company mines primarily lignite for electric utilities. Its current operations are in North Dakota, Texas, Louisiana, and Mississippi. In addition, North American Coal’s Florida operation provides dragline mining services for quarries that produce more than 18Mt/a (20 million stpy) of limerock. With more than 1.8 Gt (2 billion st)of bituminous and lignite coal re-serves in the United States, North American Coal constantly seeks new technologies to keep its operations modern, productive and cost competitive.

Jan 1, 2004